1. Field of the Invention
The invention relates to a method for determining unknown structure of a solid, and more particularly to such a method by measuring scattering waves of incident corpuscular beams or electromagnetic waves radiated to a solid having unknown structure.
2. Description of the Related Art
For determining unknown structure of a solid, the trial and error process and Fourier process had conventionally been used. In the trial and error process, the intensity of diffraction is first measured from scattering of incident X-ray beams or neutron beams, and then compared to theoretical intensity of diffraction of expected crystal structure. This step is repeated until the measured intensity is coincident with the theoretical intensity. In Fourier process, the location of atoms are determined by Fourier transformation of diffraction intensity of a plurality of diffraction spots. These processes determine crystal structure of bulk materials in particular, but cannot avoid to have ambiguity or obscurity in determining a structure of a soil d because it is necessary in the trial and error process to assume in advance a crystal structure, and because Fourier process has to select the finite number of diffraction spots.
There has been used another method for determination of unknown structure of a solid. In this method, electrons are first radiated over a surface of the crystal structure or a thin film, and then the intensity of scattering waves and the direction in which the scattering waves travel led are measured. The structure of the surface or thin film can be determined by analyzing the measurements. In particular, the low-energy electron diffraction (LEED) and the reflection high-energy electron diffraction (RHEED) are well known. As is known in the art, in LEED process, electrons having energy in the range of 20-500 eV are radiated perpendicularly to a surface of a crystal structure, and then reflected electron waves are obtained. These reflected electron waves represent data about the structure of several atom layers disposed slightly below the surface. In RHEED process, electrons having energy of 20-50 KeV are radiated quite close to a surface of an object, and then there can be obtained reflected waves representing data about the structure of atom layers disposed slightly below the surface.
In these processes for analyzing an unknown structure of a solid, energy of incident electrons are varied to measure the intensity of diffraction spots of reflected electrons. More specifically, so-called I-V curve which is a function of energy of the incident electrons is obtained by virtue of data represented by the reflected electrons, and is observed. Then, a structure of crystal is assumed, scattering intensity of corresponding electrons is calculated, and finally the assumed structure is compared to the calculation. This procedure is repeated until the assumed structure is coincident with the calculation. It often takes more than a year to analyze a structure in these processes. If an object has an increased number of atoms, it is almost impossible to exactly determine a structure of the object. In addition, incident energy is varied in these processes to avoid obscurity in determining the structure, however, scattering conditions are also varied together with the incident energy, which may prevent determination of unique structure.